Having the strings half an inch or slightly more over the body top works for me. Much more would load the top just where I want it to move. We tested it with an FFT graph. On the low E string, the fundamental was very weak but the second harmonic was huge, We compared it to a string bass. The second harmonic was larger than the fundamental on the string bass but the fundamental was much larger and the harmonic much smaller than on on the guitar. The total power seemed to be about the same.

I don't have any experience with the A bracing. I designed mine to be firm around the bridge but loose at the edges to get as large a moving piston as I could. The X-brace seems to be a very good design to do that and does a good job of supporting the string tension.

Since this is a completely experimental instrument, I've come up with a bracing plan to hopefully let the top move to increase low frequency volume. The long vertical braces will have a long notch cut into them, spanning the lower half of the top, and glued for an inch or two at the end. Crossing underneath this will be a thin (~3/16"), wide (~3/4") transverse brace from one side to the other, reinforcing across the top grain (which seems quite weak in the hemlock), but flexible enough for movement in and out.

Any comments? Might this work, or are there cogent reasons it will probably be a disaster?

If the tailblock and heelblock make a right angle with the top, then the back has to be slightly longer than the top, which is 30". By using either 5/{sin[arctan (5/30)]} or the Pythagorean theorum, it comes out to 30.414". I suppose the extra length should be stretched out over the whole back, but I just added it to the straight parts in the middle, keeping the upper and lower curves the same.

I don't know how to calculate the widths of the sides at different points, especially near where they meet the end blocks, so when the time comes I'll temporarily attach the top and back together with the head and heel blocks, and draw out a template.